1. Field of the Invention
The present invention relates to the telecommunications field, in particular to a mobile telephone communication method.
More in particular, the method according to the invention applies to terminals which are capable of connecting through radio waves to a network distributed over a territory, typically with cellular coverage, and which need to signal their position within that area during a voice call.
2. Present State of the Art
An increasing number of the latest mobile terminals include a receiver for detecting their position, e.g. of the GPS, a-GPS, etc. type, thus offering the user services based on geographic localization, such as map look-up, searching for points of interest, assisted navigation, and georeferencing of multimedia contents.
In some situations it is necessary or desirable to know the geographic position of the called terminal with some accuracy.
This requirement may be felt, for example, when a user needing assistance, e.g. because he/she cannot move, does not exactly know his/her own geographic coordinates and needs help, e.g. on a ski slope. Or when the user cannot make any calls with his/her mobile terminal because, for example, he/she has no credit left on his/her prepaid card.
In other situations it may be useful to localize a called terminal installed in a mobile means, such as a vehicle, that must be localized, e.g. in the event of a theft or an accident.
In other situations, it may be desirable that a calling terminal and a called terminal make known to each other their respective geographic positions; for example, two users in unknown places who want to meet will find it useful to be able to obtain information about their reciprocal positions.
Mobile telephone terminals are known in the art which can transmit their position during emergency calls. International patent application No. WO 2008/085993 describes an LTE telephone device equipped with a localization device, e.g. a GPS receiver, which uses position information in order to connect more efficiently to the network. The terminal described in said patent application can also enter information about its position into connection messages generated during emergency calls, so that the caller's position can be determined as quickly as possible.
In the system described in said international patent application, only the calling terminal is given the possibility to communicate its position to emergency management services. However, no information can be obtained about the geographic position of the called terminal.
U.S. patent application US 2008/0009293 describes a method for informing the calling user about the network to which the called terminal is locked. Upon requesting the call, the calling terminal apprehends if the called terminal is abroad and which network it is currently registered with. The calling user can thus decide to give up the call so as to prevent the called user from incurring in connection costs or, if the called user is in a different time zone, to avoid calling him/her at improper times.
In such a system, the calling terminal interrogates a database in the network of the operator of the called terminal to obtain the identification information of the network to which the called terminal is connected (network identifier). However, the caller receives no accurate information about the geographic coordinates of the called terminal.
FIG. 1 shows a simplified diagram of a typical mobile communication system. The system shown in FIG. 1 comprises a calling mobile terminal M1 connected through a radio-wave interface to a first base station B1, which in turn is connected to a first communication network R1 operated by a first service provider. The system also comprises a second called mobile terminal M2 connected through a radio-wave interface to a second base station B2, which in turn is connected to a second communication network R2 operated by a second service provider.
The communication networks R1,R2 typically include a plurality of network elements. In the case of the GSM (Global System for Mobile Communications) standard, which is currently the most widespread standard for mobile communications, said network elements may include traffic switching elements such as Mobile Switching Centers (MSC), terminal mobility management elements such as Home Location Registers (HLR) and Visitor Location Registers (VLR), and mobile terminal authentication elements known as Authentication Centers (AuC).
In the case of a UMTS (Universal Mobile Telecommunication System) system, said elements may include control and traffic switching elements such as Radio Network Controllers (RNC), terminal mobility management elements such as Home Location Registers (HLR) and Visitor Location Registers (VLR), and mobile terminal authentication elements known as Authentication Centers (AuC).
For a detailed description of the architecture of a GSM or UMTS system, see for example the 3GPP TS 23.002 technical specification.
In FIG. 1, the communication networks R1,R2 communicate with each other through a communication channel C; in reality, said channel may comprise several wired or wireless communication networks.
FIG. 1 illustrates a generic case wherein the two mobile terminals M1, M2 are connected to distinct communication networks R1,R2, respectively. Of course, the calling terminal M1 and the called terminal M2 may occasionally be connected to the same communication network, in which case the first communication network R1 and the second communication network R2 will coincide and the operations described below will be carried out by a single network communicating with both terminals M1, M2.
FIG. 2 illustrates a procedure for establishing a connection between the elements shown in FIG. 1, i.e. the calling terminal M1, connected to a first communication network R1, and the called terminal M2, connected to a second communication network R2, as described in the 3GPP standard, in particular in the 3GPP TS 24.008 technical specification.
When there are no voice calls, the mobile terminals M1 and M2 are in the inactive state (commonly known as “idle”), whereas when voice calls are established the terminals switch to the active state (known as “connected”).
When in the inactive state, a mobile terminal performs a number of operations, such as monitoring a radio channel known as paging channel, or PCH, and/or the broadcast channel, or BCH. The paging channel is typically used by a communication network in order to signal a voice call request to a mobile terminal. The request is broadcast in the cell or group of cells where the mobile terminal to which said call is addressed is located.
When the calling terminal M1 wants to make a voice call to the called terminal M2, a radio resource connection procedure (hereafter called “RR procedure”) is carried out, during which messages are exchanged between the calling terminal M1 and the first communication network R1. After the RR procedure has been successfully completed, a control procedure (“CC procedure”) is carried out which allows the voice call to be established. During the CC procedure, a series of messages are exchanged among the calling terminal M1, the first communication network R1, the called terminal M2 and the second communication network R2.
In particular, during the CC procedure the calling terminal M1 sends a connection start message (“CC setup”) to the first communication network R1. Two different alert messages (“CC alerting” messages) are also sent during the CC procedure to signal that the called terminal M2 is alerting the user about the call request by ringing, vibrating or by any other signalling means. The first “CC alerting” message is sent by the called terminal M2 to the second communication network R2, whereas the second “CC alerting” message is sent by the first communication network R1 to the calling terminal M1.
In the 3GPP standard, the “CC alerting” message is made up of six different information elements.
If the called user accepts the call request, a connection message (“CC connect” message) is sent by the called terminal M2 to the second communication network R2. A similar message is then sent by the first communication network R1 to the calling terminal M1 to notify the latter that the call request has been accepted. In the 3GPP standard, the “CC connect” message is made up of eight different information elements.
FIG. 3 illustrates the format in which a geographic position of a mobile terminal is transmitted, as provided for by the 3GPP standard in the 3GPP TS 23.032 specification. According to this specification, the maximum number of bytes (or octets) is 14, which include information about latitude (octets 2,3,4), longitude (octets 5,6,7), altitude (octets 8 and 9) and uncertainty (octets 10, 11, 13).